Trailers have been used over the years to supplement the carrying capacity of many different types of vehicles. Typically, trailers include a frame which is supported by one or more wheels on opposing sides of the trailer. The number of wheels used to support the trailer frame varies according to the load which must be carried out by the trailer, the trailer's length and the stability required for the particular application, and may require from one to as many as four or five wheels on either side of the trailer to provide adequate support.
Although a trailer can be an effective means of increasing the load capacity of a vehicle, the use of a trailer may hinder numerous performance characteristics of the towing vehicle. This is primarily due to the fact that the towing vehicle must provide driving power and traction for itself and the increased load caused by trailer drag. For example, the towing vehicle will often experience a loss of traction or will not provide sufficient power to pull the trailer up moderate to steep grades. When operating over adverse terrain, the towing vehicle will often experience a pushing and pulling effect as the trailer climbs over and descends small hills or passes over obstacles, causing a reduction in control of the towing vehicle and discomfort to its operators and passengers. Similarly, towing over soft surfaces, such as mud, gravel or sand, causes a substantial increase in load to both the towing vehicle and the trailer so that in many cases transport will become impossible. Of course, any combination of the foregoing adverse conditions, as is often the case, will hinder performance of the towing vehicle still further.
Additional problems associated with towing of trailers are experienced by vehicles designed for use over adverse terrain. Such vehicles often utilize either a plurality of wheels or a track to support the opposite sides of the vehicle. The wheels or the tracts on each side of the vehicle are driven independently to allow the vehicle to be maneuvered by skid steering. Such vehicles experience increased drag during turning due to lateral sliding of their wheels or tracks over the underlying surface as the vehicle pivots. Drag imposed by a trailer hinders such pivoting of the vehicle, resulting in reduced maneuverability. This is particularly true when the trailer utilizes two or more wheels on each side thereof. In this circumstance, the trailer imposes additional drag during turning caused by lateral sliding of its front and rear wheels over the underlying surface in a manner similar to skid steering of the towing vehicle.
The present invention provides a control system for powering a trailer which eliminates many of the foregoing and other problems associated with conventional trailers. The system includes one or more hydraulic motors mounted on a trailer frame for driving one or more wheels mounted on opposing sides of the trailer. Pressurized hydraulic fluid supplied to the hydraulic motors on the trailer from a hydraulic pump on the towing vehicle selectively powers the trailer thereby reducing the drag imposed on the towing vehicle.
In one aspect of the invention, at least two hydraulic motors are used, each for driving one or more wheel members on opposing sides of the trailer. The hydraulic motors are supplied with pressurized hydraulic fluid in parallel from a common supply line, such that the speed of the motor associated with the inward side of the trailer will decrease and the speed of hydraulic motor associated with the outward side of the trailer will increase during turning. This feature reduces drag associated with pivoting the trailer on a centrally located axis.
In another aspect of the invention, the hydraulic pump on the towing vehicle is a variable displacement hydraulic pump. Displacement control apparatus is provided for varying the displacement of the hydraulic pump to maintain the hydraulic fluid supplied to the hydraulic motors at a predetermined pressure. This feature allows the speed of the trailer to vary during towing without a corresponding variance in the driving force generated by the hydraulic motors.
In yet another aspect of the present invention, pressure control apparatus is included for varying the pressure of the hydraulic fluids supplied to the hydraulic motors.
In still another aspect of the present invention, the hydraulic pump may be mounted within a command vehicle which tows the trailer. Structure is provided within the trailer for providing pressurized hydraulic fluid from the hydraulic pump to the hydraulic motors. This feature increases serviceability of the system.
In yet another aspect of the present invention, wheel member positioning structure is provided for varying the vertical positioning of the trailer wheels with respect to the trailer frame. This feature allows a variance in the overall height of the trailer, thereby facilitating loading and unloading of its load. In addition, this feature allows vertical positioning of the wheels to distribute the trailer load in a manner facilitating turning of the trailer.